This application relates to copending applications entitled xe2x80x9cMethod and Apparatus For Light to Frequency Conversionxe2x80x9d, inventor William W. Wiles, Jr. (Attorney Docket 26783.18) and xe2x80x9cMethod and Integrated Circuit For Temperature Coefficient Compensationxe2x80x9d, inventor William W. Wiles, Jr. (Attorney Docket 26783.20), filed concurrently herewith, assigned to the assignee of the present disclosure, and incorporated herein by reference.
The present invention relates generally to semiconductor devices, and more particularly, to a method and integrated circuit for bandgap trimming.
A number of optoelectronic systems applications require an accurate measurement of the intensity of a light beam or incident light, the measurement being performed over large ranges of input signal amplitude and wavelength. It is desired that the measurement accuracy be maintained over a wide range of environmental conditions. In addition, it is desired that the measurement be made in a minimal volume as dictated by packaging considerations and at a cost commensurate with consumer type systems.
Typical system requirements dictate that an incident light intensity needs to be converted to a digital form for use by a digital processor. To accomplish this, the light intensity is converted to an electrical form that can be digitized. For example, one technique applicable to sampled data processor systems includes converting the light intensity to a voltage that can be applied to an A/D Converter (ADC). This method however requires an additional analog block (i.e., the ADC), but can be used in those applications requiring a higher bandwidth. A second technique, applicable to very low bandwidth applications, includes directly converting the light intensity into a frequency that can be counted by a digital processor.
U.S. Pat. No. 5,850,195 entitled xe2x80x9cMONOLITHIC LIGHT-TO-DIGITAL SIGNAL CONVERTER,xe2x80x9d issued Dec. 15, 1998, discloses a converter having a switched capacitor oscillator in which the reference function is included in the oscillator circuit. The switched capacitor oscillator requires that calibration be accomplished by trimming the capacitors of the oscillator. However, the oscillator has a high level of parasitic capacitance which limits its high frequency performance. In addition, certain applications, including infrared incident intensity, for example, require a different temperature coefficient which cannot be implemented in an efficient manner in the oscillator circuit of the ""195 converter.
It would be desirable to provide a method and integrated circuit for bandgap trimming for overcoming the problems in the art.
According to one embodiment of the present disclosure, an integrated circuit for generating a bandgap reference voltage (VBG) includes a first circuit and a second circuit. The first circuit includes an op-amp for equalizing emitter currents of a first bandgap transistor and a second bandgap transistor. The second circuit trims out error in at least one emitter current to achieve a desired frequency tolerance. The second circuit includes at least a single transistor digital to analog converter (DAC). A method for generating a bandgap reference voltage (VBG) is also disclosed.